Novel interactions between urokinase and its receptor.

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Medicine

Background:

• Urokinase-type plasminogen activator (uPA) and its receptor (uPAR) form complexes with varying affinities.
• uPA/uPAR complex functions include catalytic activity and signal transduction, observed at different concentrations.

Purpose of the Study:

• To investigate novel interactions between uPA and soluble uPAR (suPAR) at supra-saturating concentrations.
• To elucidate the role of suPAR oligomerization in modulating uPA binding and activity.

Main Methods:

• Dynamic light scattering, gel filtration, and electron microscopy to analyze suPAR structure.
• Biacore assays to determine binding affinities of uPA to suPAR forms.
• Enzyme activity assays for scuPA/suPAR and tcuPA/suPAR complexes.

Main Results:

• suPAR exists in monomer, dimer, and oligomer forms.
• High concentrations of uPA and suPAR induce novel interactions, increasing complex activity.
• scuPA binding causes dissociation of suPAR dimers/oligomers, with reduced affinity for these forms compared to monomers.
• uPA binding to suPAR dimers/oligomers shows lower affinity than to monomers.

Conclusions:

• uPAR exists in an equilibrium of monomeric, dimeric, and oligomeric states.
• These novel interactions and varying affinities regulate uPA/uPAR complex activity.
• The findings suggest a new mechanism for uPA/uPAR-mediated signal transduction.